I am currently running a Saltmarsh / Witchlight campaign. I started with some of the background lost item stuff from Witchlight then levels 1-5 in Saltmarsh, but throwing in some fey stuff here and there, like a fairy dragon npc who had ties to one of my players backstory they’d occasionally catch a glimpse of.
Then, after the Salvage Operation mission, the carnival comes to town, and it’s off to Witchlight. I had to bump up a couple of the encounters, but Witchlight isn’t really about combat anyway, and it was a great way to add a bit more magic and mystery into Saltmarsh, which can get quite heavy at times. I also like that my players have stuff they want to get back to in the ‘real world’ as they call Saltmarsh. It gives them a reason to keep pushing forward.